Electroplating method and product



Jan. 3l, 1939, H. H. ARMSTRONG ET Ar. 2,145,745

ELETROPLATING METHOD AND PRODUCT Filed: Sept 18, 1934 A TTORNE Y.

inet-medv Jim. 31,. 1939 uNlflED STATES .PATENT OFFICE z;145.'z4sl f l l Harry-Howard Armstrong and Arthur Burley l Menefee, Beverly Bills, Calif., assignors to Tungsten Electrodeposit Corporation, Washington, D. C., a corporation oi' Delaware v.Applicationseptemim,111, 1934, sei-m No. 144,566

18 Claims.

yOurinvention relates to a process `for electroplating tungsten alloys i'rom 'aqueous solutions, and alloys of metals other than tungstenv from f the same type of electrolyte. 5 The object of our invention is theproduction of 'tungsten alloy plates, of dense, closely adherent quality which are highly resistant to the corrosive action of acids and saltsand withstand high temperature. l Up yto the presenttime, tungsten -or tungsten any disclosed methods have been .far from being resistant to strong acids, have been produced-from decidedly alkaline electrolytes (pH 9 l to 13), high current densities have been required (75 to 400 amperes per square foot of submerged cathode area) with excessive evolution of hydrogen at the cathode, and in most cases less than 1% currentefilciency. I v Our invention specifically relates to alpractical and economical method of producing tungsten alloy plate, of variable tungsten content, which may'be applied by means of standard equipment and common reagents,- and which maybe 5 controlled and operated as contiruinusly and readily as are the conventional nickel, chrome,

cadmium, etc., processes.v

As compared withv the now known and disclosed methods of plating tungsten, our method.

m, 4embodies the following advantages:

y 1. The 4production of highly acid resistant s plates; l s 2. The production of tungsten alloy plates of variable tungsten content (within reasonable 3,-, limits); thus giving a wider iield oi application;

3. The production of a 'series of tungsten alloys, of variable tungsten content, and variable content of the metal or metals alloyed with the tungsten; .m 4. Satisfactory anode corrosion;

5. A pH range not too critical for easy control,

.The figure is a diagrammatic view ofl a cell which may be utilized in practicing the'invention. l

. Referring to the. drawing, I is the cell box :.5 within which are placed an anode oranodes or cathode or cathodes 2 and 3, respectively.- Wires 4 and'5 lead from the anode andcathode respectively,.to asource ofv current supply ,'6. As

is customary, the cell box is adapted to hold 4an (m electrolyte '|.v It may be desirableto agitate the ed to between or some 'other alkaline reagent.

(Ci. 204.--2l

electrolyte, and this may be done through the able source of current supply (not'shwn). alloy plates, which have been produced by known v As descriptive of our process, approximately 4% by weight of NAHP; 'or KHF; or the equivalent amountV o1' HF is dissolved in 100 parts of waterand approximately 5% by weight of NaCl and 1% by weight offconcentrated HCl is added to the solution. .This solution is then heated to between 40 and 75 C. or higher,v and electrolyzedfor two hours or longer at 11/2 t'o 6 volts or higher, using a tungsten carbide, a tungsten y alloy carbide, such as tungsten-nickel carbide or a tungsten anode, and any good conducting cathode,. such AasCu, brass, etc. During this treatment, the electrolyte turns a rich brown color, dueto'the corrosion of the anode and the going intol the solution of a soluble tungsten salt, and we believe this to be in the form oi' tungsten dioxide (W02). If a tungsten alloy carbide anode,` such as tungsten-nickel, tungsten-cobalt, etc., has not been used, we then add approximately two-tenths of one per cent. (.2 of

- 1%) by weight'or more of a metal in the form oi' an acid soluble salt, the metal of which is to-be alloyed with the tungsten in the plate, such as NiCh,2NiC03-3Nl (OH) 24H20 or Ni (OH) s,

l etc. When this is dissolved', the pH of the solution is usually below 4. 'I'he pH is then adjust- 4.5 and 6.8 bythe Aadditionof o y Na(OH) K2(OH) The temperature of the solution is kept between 35 and 85 C. or even higher. The cathode to be plated is then placed in the solution, and electrolyzed at approximately 14 amperes per square foot of submerged cathode area. Small vadditions of the acid soluble salts of the metal or metals to be alloyed with the tungsten are'required from time to time as the solution becomes vdepleted of these salts. Where a tungsten-nickel carbide anode is used,

y the addition oi' the acid soluble nickel salt is rarely necessary, as. the, corrosion of the anode is Y suiilcient to give the necessary amounts or the two metals for satisfactory plating conditions.

We, have found that it is possible to dilute'the above solution 50% or more and still obtain satis-- factory plates, slightly varying the voltage and current density.

Preferably Na(OH) and'HCl are used as reagents for the control of the pH of the electrolyte.

2 e Howeverjvarious other acids and bases. can be used without detrimental effects. For dense acid resistant lplate, we have secured the best resultsl at a pH between 5 and 6. It is possible to obtain bright metallic deposits below 5 and up to approximately 10. From a' pHof the 6.8 and` above,

it is advisable to have present in the solution suiiicient sugars, or weak organic acids, in order to prevent the precipitation of such metals as Ni, Co, etc., when these metals are to be alloyed with the tungsten.

While we have obtained bright metallic deposits throughout a currentdensity range of from 6 to 35 and even higher amperes per square foot of time become depleted in tungsten. It then becomes necessary to build up the tungsten content by electrolyzing at a more acid pH than .it-will plate, or by the addition of tungsten dlioxide (WO2), as described later. v

Above we have described one method of producing tungsten alloy deposits. Another way to produce an electrolyte, from which tungsten alloys can be deposited, is by dissolving tungsten dioxide (WO2) in the same type of electrolytes as described above, then following the same procedure as above as regards pH, current density, temperature, addition of acid solublemetal salts,

vwhich-are to be alloyed with the tungsten, and

using tungsten or tungsten carbide alloy anodes, oreven, inert conductive anodes, such as platinum or carbon.

For restoring the tungsten content of depleted solution, we prefer either to acidify' with acid uorides or hydrouorlc acid to a pH o1 approximately 4, then electrolyze or to add WO2 dissolved in acid fluorides or hydroiluoric acid. After either of the above steps, it may be necessary to adjust to the proper pH for plating conditions. Undoubtedly many of the acid soluble salts containing the WO2 radical, such as 2NaF-WD2F2; KF-WO2F22H2O; NHlF-WOzFz-HzO, etc., `could be used for reviving depleted solutions. 'Ihese salts, however; are difiicult to prepare, costly, and usually unstable. In describing the above, it is to be understood that our invention is not intended to be limited to the production of tungsten alloy deposits, 'as the following single metals (Ni, Co, Sb, Zn, Cd, Aq, Hg, and Sn) have been plated through substantially the same acid fluoride bath as -above described, by either straight anode corrosions or adding acid soluble salts of the metals. Also, a chrome-nickel alloy has been produced under approximately the same conditions, and

our results indicate that many other alloys, such as nickel-chrome-iron, chrome-iron,- manganeseiron, etc., can be produced.'

Nor is it intended that our invention be limited to the use of the specific lreagents mentioned. For sample, sodium-or potassium hydroxide, plus hydrouoric, to produce the approximate equivalent oi the acid iiuorides can be used.` Also various strengths ofhydrouoric acid can beelectrolyzed withl tungsten, tungsten carbide, or tungsten-alloy carbide anodes ,then brought to the.

proper WO2 ion concentration by dilution or concentration as required.V It is to be understood that the sodium chloride and hydrochloric acids are not essential to the operation of the process, being addedprimarily to increase the conductivity of the bath, and increase anode corrosion. Also, various' reagents, ammonium hydroxide, beryllium hydroxide, lithium hydroxide, lithium carbonate, boric acid, etc., may be used as pH form acid iiuorides, such as NiF2-5HF-6H2O,

CoF2-5HF- 6H20, etc., or those metals which form two luorides, such as SbFa and SbF5, CuFa-2H2O and CuzFa, CrFaand CrFz, etc., will, under substantially the same conditions as y'described above,

alloy with the tungsten as a metallic and adherent plate.

So far as we are aware, tungsten carbide orv tungsten carbide alloy anodes have not been employed or suggested by past disclosures or used by operators. Nor do We find any suggestion or disclosures of the use of tungsten dioxide (W02) dissolved in any acid electrolyte. Nor do we find any mention or suggestion of any direct attempt to produce tungsten alloys, where the soluble metal salt, the metal of which to be alloyed with l tungsten, is added to the electrolyte for the direct purpose of producing tungsten alloy plates of variable tungsten content, suitable for various specific purposes.

We find with tungsten-nickel deposits. that when very small amounts of the soluble nickel 4salt are present in the ,electrolyteusually higher than ordinary current density is required, and that the plates so produced are not as dense and therefore less acid resistant than plates produced from the same solution after the addition of more soluble Ynickel salt. As the amount of soluble nickel salt is increased higher and higher, the plate becomes less and less'acid resistant. An appreciable amount of acid soluble nickel salt must be present in the electrolyte and anappreciable amount of metallic nickel must actually plate out alloyed with the tungsten before the best acid resistant deposit is obtained. This may be due possibly to the fact that in a certain range of proportions of the two metals,l the alloy is more acid resistant, or that certain amounts-of nickel must be present in order to produce a dense, closely adherent deposit.

'I'he theory of our invention is believed to be as follows; y Y We quote Mellor for the existence of the following dioxyi'luoride salts of tungsten:

and also there are mentioned the double dioxyfluoride salts ofCd, Th, Co, and Ni. Also quoting from Mellor, Mariguac states that when normal or metatung'states are dissolved in hydroiluoric acid, compounds of the metal iiuorides with tungsten dioxyfluorides are formed. These salts are usually soluble in water.

It seems reasonable to `believe in our invention that electrolyzing tungsten, tungsten carbide, or

tungsten alloy carbide anodes in an acid bath containing iluorine ondissolving WO: in an acid ',iluoride solution, the radical (WOzFn) 'is formed..

The solutions in both cases, under normal plating conditions, are a rich brown color.

Assuming'- Athat the dioxyiluoride (Woah) is formed, it would ionize as fI-he two-valence of the (WO2) is as lowla valence as any'oxlde of tungsten, plus being the lowest oxide of tungsten that we are sure exists as an. -individual compound. In any case, vwe believe wev are dealing with a tungsten ion in our elecf trolyte in a low state of oxidation, and more easily We, however, have so far beenunable to produce a deposit in any acid solution .except when fluorine was present. The fact leads us-to believe that the tungsten will only plate from the radical `(WOzx) ++(F2) and further to the possibility (taking into account the fact that there must be present an acidv soluble salt ofv some metal,

- which will plate out of the solution, alloyed with the tungsten) that in order tov plate tungsten from aqueous` solutions, there must be present in the electrolyte some certain amount of a metal fluoride with tungsten dioxyfluoride, or, in other words, the equivalent of a double salt.

Knowing that Ni and Co, both formed dioxy- Ailuorideswith tungsterajand both formed acid 1uorides, we reason that any metal (that could 'i be plated from an acid iluoride electrolyte) which mal and metatungstates are dissolvedv in hydroformed an acid fluoride, or which formed two fluorides will form the equivalent'of doublefsalts,

when' dissolved in solutions containing (WO2).++,

and such metals will plate out alloyed with the tungsten, our theory beingthat the metals, which formed two fluorides, such as SbFa and SbFavCrFa and CrFz, etc., when the higher iluoride'was dissolved, that the equivalent of an acid uoride Awas produced, as SbFs when dissolved would iontheory, we proved that both Cr and Sb would plate out of the electrolyte'alloyed with the tungsten, and we believe that all metals falling under the above classifications such as Cu, Fe.,Ni, Cr, Co, Mn, Hg, As, Sn,` etc., will act the same. Our opinion of the value of the Clin the electrolyte is that it increases anode corrosion, and possibly there is formed (WO2) ++Cl thus in'- creasing the concentration of the tungstenmetal ion, which would tend to produce better and more uniform'plating conditions. v

According to Mariguacs result that when noriiuoric acid, compounds of the metal iluoride-s with tungsten dioxyfluori'des .are formed, it should be possible to produce from these compounds an lelectrolyte from which ytungsten alloys could be plated. Our experience has been i'rom the attempted use of W03, various tungstates, metatungstates and paratungstates in various acid fluoride-bathathat the solutions are in all cases diilicult to control. In most cases, the solutions when heated and electrolyzed, turn blue due vto the formation probably of some WaOs coml pound and also precipitate out large' amounts of radical hydrated W03. As stated above, we prefer to use anode corrosion or WO2, l

It has been suggested by Holt. and Kahlenberg that tungsten will not plate. on tungsten. This fact, if true, would satisfactorily explain why past investigators have failed in -their efforts to develop a commercial method of plating tungsten. i

Our experiments and 'results prove that various tungsten alloys will plate in a dense, adherent deposit on many metals and alloys, as well as on A themselves.

tions, the cathode rst .turns brown or blue due,

we'believe, t'o an/oxide illm, before it becomes metallic looking. In other words, the oxide is first formed and then reduced. This would not tend to produce a dense deposit. Also, with high alkaline electrolytes, it is necessary to use high current densities, with correspondingly high evo. lution of hydrogen'at the cathode. i This condition tends to produce pitting, and a plate, which is not dense, and therefore not as acid resistant.

Wey have noted in testing the acid resistant qualities of our tungsten alloy plates, that'in some cases (for instance, the plating over copper, brass,

or iron flashed with cadmium) the results indicate better acid resistant coatings (tungsten-nickel alloy over cadmium) than .would be expected considering the distance apart in the electrometive series, of cadmium and aV high percentage tungsten alloy. 'I'his leads to the possibility that tungsten and tungsten alloys in contact with certain metals may have a protective quality due tosuch contact, just as platinum in contact with ic acid 100 hours or more with apparently no efi'ect on the plates or electrodes. The same type of plates have withstood cold concentrated nitric acid for eleven hours before definitely breaking down.

It is known that tungsten when heated to l500 Il'. or perhaps much lower, in the presence of carbon or in a carbonizing atmosphere, will be converted to a carbide. At higher temperatures, this change is much more rapid than at lower temperatures.

We do not ilnd used or disclosed in documents or industry any lmention of the use of tungsten or tungsten alloy plates being converted to carbides, (with approximately 9.5 hardness, diamond by subjecting such plates to heat in the presence of carbon, or in a hot carbonizing atsurface is required, such as valves, ,valve seats. cylinder walls ci' internal combustion engines. pump lines, engine ports, gun barrels, etc. ln

case such lplates are used, .as valves, cylinder walls, gun barrels, etc., where heat and carboniaingatmospheres are a-naturalcondition under operating conditions, we believe the tungsten alloy plate will gradually be converted to a carbide. For other uses, the plate would be converted tola carbide by a separate treatment.

plates, for instance, when deposited by our prochydrochloric or sulphuric.

ess on chrome plated ca hodes, do not closely adhere to said' catho'des, but deposit in scales and flakes, which are readily scraped or brushed free crystals to tungsten oxide (W03).

-It, therefore, is advisable in producing pure tungsten crystals -to deposit the tungsten alloyed with a metalwhich is either volatile and can be freed from the tungsten by. heat, or one .which is readily soluble in a single acid, preferably sible to .produce substantiallypure fine-grained metallic tungsten crystals, free from metal or oxide impurities.

We claim: v

l. The method of putting tungsteni'rom a tungsten carbidev anode into solution, which conf sists in causing electrolytlc corrosion of the tungsten carbide anode vin aqueous acid solution containinga iiuoride ion. l 2. The method of putting a metal to be alloyed 'with tungsten vinto solution, which consists in causing electrolytic corrosion of a tungstic alloy carbide anode in an aqueous acid solution containing a iluoride ion. A

3. The process of electroplating with tungsten l' alloys, which comprises electrolyzing tungsten suiiicient lengtli of time to build up the ion conu carbide anodes in an aqueous acid iiuoride bath, to produce available tungsten ions in said bath; adding an acid soluble 'salt of a metal of group 8, series 4 of the periodic table to be alloyed with the tungsten to said bath, adjusting the pH of said bath to between 4.5 to 6.8; maintaining the solution at a temperature between 35 C. to 80 C., with a current density of about 14 amp eres per square foot of submerged cathode area. 4. The process of electroplating with tungsten alloys, which comprises electrolyzing tungsten alloy carbide ano'des -in an aqueous acid iuoride bath, to produce available tungsten ions in said bath; adding an acid soluble salt of a metal of group 8, series 4 of the periodic table to be alloyed with the tungsten to said bath, adjusting the pH of` said bath to; between 4.5 to 6.8; maintaining the solution at a temperature between 35 C. to 80 C., with a current density of about 14 amperes per square foot of submerged cathode.

area.

5. 'I'he process of electroplating with tungsten alloys, which comprises dissolving tungsten dioxide WO: in an Yaqueous acid fluoride bath to produce available tungsten ions in said bath; adding an acid soluble salt of a )metal of group 8,

series 4 of the periodic table to be alloyed with the tungsten to said bath, adjusting the pH of said bath to between 4.5 to 6.8; maintaining the solution at a temperature between 35 C. to 80 C., with a current density ofabout 14 amperes per square foot of submerged cathode area-.-

6. A process for producing tungsten nickel alloy plates consisting of electrolyzing tungsten containing alloy anodes in an acid fluoride bath a cntration of the metals in the alloy anodes, for

In this way, it is pos- 2,145,745 We have noted that tungsten-nickel alloy.

good lplating conditions, adding to the solution a quantity of an acid solublenickel salt, then adjusting the pH to between f4.5 and 6.8 and electrolyzing at temperatures of from 35 C. to 80 C. at current densities of vfrom '6 to 35 amperes per square foot ofl submerged cathode area.

7. A process of electroplating tungsten nickel alloys which' comprises electrolyzing an acid bath containinga iluorlde and available tungsten and nickel ions.

8. That method of preparing an electroplating bath which comprises anodically corroding` a tungsten containing electrode in contact with an aqueousv acid solution containing a uoride, adding a compound containing available nickel, adjusting the pH of the solution to between 4 and a suitable metallic cathode.

9. An electroplating bath for electrodepositing tungsten alloys comprising an aqueous solution formed by dissolving tungsten dioxide /in an aqueous solution of an alkali biiluoride and adding thereto a solution containing a soluble salt of a metal of group 8, series 4 of the periodic table.

10. A method of producing tungsten alloys of variable tungsten content which comprises dissolving a tungsten containing compound in a hot aqueous solution of an alkali acid uoride, adding thereto a salt of a metal o'f group 8,series 4 of the periodic table, and electrolyzing the solution while it is maintained definitely acid to codeposit tungsten and said second metal from the solution.

11. The process of electroplating with tungsten alloys which comprises electrolyzing a tungsten containing anode in an aqueous acid uoride bath to produce in said bath availablel tungstenV ions, adding to the batha soluble salt oi a metaloi group 8, series 4 of the periodic table, while maintaining the bath at a pH oi' between approximately 4 and 6.8 and at elevated temperatures,

and then plating out a tungsten alloy from the bath upon a metal cathode.

12. An electrolyte bath for producing'alloys by .i

codeposition of tungsten with other metals, comprising an aqueous acid solution containing a fluoride together with available tungsten ions and ions of a metal of group 8, series 4 of the periodic table, and an organic acid.

13. A process for arresting and preventing corrosion of metals, which consists in rst electro- 6.8 and plating out a tungsten nickel -alloy upon plating said metal with a metal close to it in the l electromotive series, `then immersing the preliminarily plated metal as a cathode in an aqueous uoride bath having an acid reaction, which bath contains ions of tungsten and ions of a metal of group 8, series 4 oi' the periodic table.

14. An electrolyte bath for producing alloys by codeposition of tungsten with other metals comprising an aqueous acid solution containing availableiiuoride ions together with available tungsten ions and ions of a 'metal of group 8, series 4 of the periodictable.

l5. A method of producing tungsten alloys of "variable tungsten content by electrodeposition from an aqueous solution comprising, establishving an aqueous solution of deilnite acidity containing iiuoride ions, ions of tungsten and ions of a metal of group 8, series 4 of the periodic table, and controlling the amount of tungsten in the alloy deposit by varying the metal ion concenf tration in the bath of the metal to be alloyedA with the tungsten. f

16. A method of producing electrodeposited plates c! tungsten which comprises electrolyzing a tungsten-containing anode in an aqueous, strongly acid bath which contains uoride ionsand ions of a metal of group 8, series 4 of the periodic table, and then plating out tungsten from the bath at a lower acid concentration.' v

17. A method of preparing an aqueous electrolyte forthe electrodepositing of tungsten which 'comprises electroiyzing a tungsten containing anode in an aqueous solution of an acid iiuoride at a pH oi substantially 4, adding to the bath a salt of a metal ot group 8, series 4 of the periodic table, then adjusting the :acidconcentration to approximately a pH oi' 4.5 to 6.8.

18. A method of preparing an velectrolyte from which tungsten may be' eiectrodeposited which comprises, electrolytically corroding a tungstencontaining anode in contact with aqueous hydrochloric acid, adding to the bath a fluoride and a soluble salt oi a metal of group 8. series 4 oi the periodic table.

HARRY HOWARD ARMSTRONG. BURLEY MENEFEE.' 

